Police detained 14 young extreme right activists after they torched tyres and tried to block migrants in the French port of Calais from entering the centre of town.
The group Generation Identitaire said in a statement that its activists "took control" of two bridges on Saturday and wants EU and national governments to reinstate borders.
The regional police department said 14 were detained and a vehicle seized to show the government's "determination not to let extremist movements manipulate the migrant crisis".
Calais, long a magnet for migrants trying to sneak across the English Channel to Britain, became a flashpoint in Europe's unprecedented wave of migrant arrivals.
Thousands of people escaping war and poverty in the Middle East and Africa gathered in a filthy Calais camp that authorities are gradually dismantling.